Antechamber type spark plug mechanism



Aug. 31, 1954 e. F. WRIGHT ANTECHAIIBER TYPE SPARK PLUG MECHANISM Filed Aug. 14, 1951 3mm GnLsEz-r F. Wmem' Patented Aug. 31, 1954 ANTECHAMBER TYPE SPARK PLUG MECHANISM Gilbert F. Wright, Renton, Wash., assignor to Boeing Airplane The spark plug mechanism according to the present invention has proven to be particularly free from fouling or burning of the and idles smoothly at lower speeds.

The spark plug mechanism of this invention is applicable to an internal combustion engine by being screwed into the usual spark plug hole,

be located in rather a particular position in the antechamber. Maximum effectiveness of the spark plug operation Company, Seattle, Wash., a corporation of Delaware Application August 14, 1951,

8 Claims. (Cl. 123-169) Serial No. 241,790

depends largely on a proper relation between various characteristics of the spark plug mechanism, and a nice balance of proportions and dimensions must be maintained between the parts of the spark plug mechanism.

More specifically, the antechainber within the spark plug mechanism is convergent toward the inner end of the spark plug, Which is the end to be exposed within the engine combustion chamer, and opens at such end through an aperture. The electrodes forming the spark gap must be located remote from the inner end of the spark plug and preferably the space behind the electrodes is small and protected by a shoulder or step formation between it and the main portion of the antechamber.

Spark plug mechanisms may be classified as either of the hot type, where heat cannot be transmitted too readily from the metal and and insulatin material of the central electrode is in quite direct contact with the shell of the spark plug mechanism, so that heat will be dissipated readily from the core. The spark plug mechanism of this invention has the unique advantage of permitting a very cold type of con struction without the usual tendency toward excessive fouling.

Especially is it a feature of the invention to form the portion of the spark plug body immediately encircling the electrode-carrying end of the ceramic core as an inner bushing separate from the outer part of the spark plug body which is mounted in the engine, so as to provide a discontinuous heat conduction path between that portion of the spark plug cavity Wall adjacent to the electrode-carrying core end the engine block. The spark plug body is inserted into the plug port, such as bein screwed therein, sufficiently far as to provide a relatively short heat conduction path from the ceramic spark plug body should be inserted into the engine port at least substantially to the inner end, of the inner spark plug body part or bushing circling of the spark plug body the former should fit loosely within a cavity in the latter.

Additional features and advantages of the spark plug mechanism will be pointed out in the following detailed description of representative forms shown in the accompanying drawings.

Figure 1 is a longitudinal sectional view through a spark plug constructed in accordance with the invention, and Figure 2 is an exploded perspective view with portions. broken away to show internal construction.

The drawing shows a spark plug incorporating the invention which is intended to be screweddirectly into the spark plug hole or port of an internal combustion engine and incorporates an antechamber. The spark plug body or shell 5' has an externally threaded inner end portion it of a standard size to screw into the usual port or spark plug hole of an internal combustion engine. The external diameter of the thread on this part may, for example, be eighteen millimeters. At the outer end of this threaded portion an erternal shoulder H, and slightly farther from the inner end It of the spark plug, that is the end adapted. to be exposed within the engines combustion space, is an internal shoulder ii Near the outer end of the shell ii is a noncircular portion 13, preferably hexagonal, to which a wrench may be applied for screwingthe threaded portion into. an. engine port or for unscrewing the plug from the engine port.

Within the body I is received a bushing 2' having. a step 20. approximately midway between its ends which bears against the internal shoulder [2. of the shell. This bushing is not threadedly connected with the body and fits loosely within the spark plug body I proper, so as to impede transfer of heat from the bushing to the outer part of the spark plug body or shell. The shell may have a further slight shoulder is against which. the inner end of bushing 2 seats, such inner bushing end being located at least substantially as close to the inner end of the plug body as the outer end of the threaded. portion H3. Preferably this bushing isof metal and its axially inner end carries the grounded electrode 2.! located immediately adjacent to the inner end face of the bushing.

The central electrode 3' is mounted in a ceramic spindle or core 3c carrying a metal band 3! threaded externally to meshwith internal threads formed in the outer endof the shell I. A spacing washer 4 is interposed between the band 3.!- and the outer end of bushing. 2., which is of selected thickness to establish the. proper width of the spark gap between the grounded electrode 2i and the central electrode 3.. The outer end of the band 3 i. has a suitable formation 32 to. receive a wrench operable to. rotate the spindle 30 relative to the shell. i 1 The outer end of the shell. is closed by a cap 5 having an externally threaded inner end complemental to. the internal thread of the shell. outwardly of this threaded end portion the sleeve has a noncircular wrench-engaging part 553 which preferably is hexagonal. This cap has a ceramic lining 5|, insulating the cap and shell from the terminal 33 on the outer end of the spindle 3h. The outer end of the cap is open for reception of an electrical conductor to engage the terminal 33, and. preferably has. external threads. 52 to. receive a protective cap or for securement of an ignition- Wire shield.

Of the parts described above the spindle 3%], central electrode 3 and terminal 33:, and the cap 5, may be conventional. The invention of; the present spark plug. mechanism resides in the bushing 2' and its relationship tothe tip of spinthese two portions.

dle 30, and further in mounting the electrode 2| on such bushing.

The formation of the antechamber within the inner end portion of the body includes a large portion and a restricted opening through the inner end MS of shell I, such opening affording communication between the large portion of the antechamber and the combustion space of the internal combustion engine. The inner walls of such large antechamber portion converge from a maximum diameter or cross sectional zone [5 toward a minimum diameter or cross sectional portion H in the restricted opening. Such con vergent walls preferably are concave and are reasonably faired' into the restricted or minimum cross sectional portion ii to promote smooth flow of gasin either direction between Preferably the antechamber is of circular cross section, but it may be noncircular.

Immediately at the side of the large portion of the antechamber away from the innerend it of the spark plug body the axially inner end of bushing 2 forms a radially inwardly projecting shoulder in the antechamber. The electrodes 2! and 3 are located substantially at such shoulder, Figure 1 showing the gap immediately at the side of such shoulder away from the orifice and body end- 15', that is axially outward from such shoulder; and within a reduced bore portion 2?; of the bushing.

The inner end or tipgrounded of the insulating spindie 30' is tapered inwardly, and inorder to provide sufiicient clearance between the bushing 2' and spindle the bore of the bushing has an enlarged portion 23- toward its axially outer i. e,

bore portion 22 at the inner end of such bushing is stepped radially inward toward the spindle to reduce the space around its inner end. The lengths and diameters of the parts of this stepped bore should be related to the" lengths and eters' of corresponding portions of the tip ofspindle 3!}- so that sufficient clearance will be left between the two at all locations axially or them to accommodate some deposit of carcsm and lead compounds from the fuel, while this space is narrow enough to keep the portion of the antechamber outwardly of the spark gap of small volume as compared to the volume of the antechamber inwardly from the spark gap;

If the inner end orifice of the antechamber is toorestricted for the size of the antechamber as a whole, the desired functioning of the spark plug mechanism will be lost. Consequently it will be helpful to describe an example of a typical spark plug mechanism made in accordance with thepresent invention of a size suitable for installation in present engines. In a so-called 18' millimeter spark plug the external diameter of the threads it on the inner end portion of the spark plug would be 18 millimeters. The minimum diameter of the restricted ori ce [1 forming the inner end of the antechamber in such case should not be less than three-sixteenths of an inch inorder' to enable sufficient gas'to flow from the engine combustion space into the antechamber and out again. On the other hand, ifthe minimum diameter of such orifice ii is more than ab'outthree- -ei'ghths of an inch, the desired nozzle eifect would not be securedand excessive fouling caused by deposit of carbon and lead compounds in the antechamber would occur.

The maximum diameter of the large portion of the antechamber l5 may be from seven-sixteenths otan inch to nine-sixteenths of an inch; an ap preciable reduction below the former value increasing the tendency for carbon and lead compounds to be deposited in the antechamber, and any appreciable increase above the latter dimension causing excessive reduction in the power produced by the engine.

stricted orifice minimum diameter of one-fourth with walls of circular arcuate curvature as described above was 0.0975 cubic of the restricted orifice 0.049 squire inch. Efllciency of the spark plug is prejudiced by making the orifice I! at the inner end of the antechamber either too small or too Also the electrodes must be remote from the restricted orifice the inwardly projecting chamber.

To reduce the tendency of carbon and lead compounds to be deposited in the space behind the end of bushing 2 which would tend to cause bypassing of the spark gap, the volume of that portion of the antechamber axially outwardly of the spark gap should be a minor portion of the volume of the entire antechamber. In fact, the volume of that portion of the antecharnber axially outwardly of the zone of maximum cross section of the antechamber should be a minor portion of the volume of the entire antechamber. In a spark plug of this type it is also preferred that the grounded electrode 2| project radially into a position overlapping the central electrode, as shown in Figure 1. It is possible, however, to employ electrodes of other types, so long as they are remote from the aperture I? and at or adjacent to the inwardly projecting shoulder of the antechamber.

The spark plug mechanism shown in Figure 1 is nominally cf the hot type because of the spacing between the central electrode spindle 30 and having an axially shorter space between the tip of the core and the nearest part embracing it, since heat cannot be conducted readily between the bushing 2 and the body I of this spark plug because of the discontinuity of these parts and the looseness of fit of bushing 2 in body i in a radial direction. While the fit of the bushing endwise may be tight, the axially engaged surfaces of the bushing and spark plug body are of small area, whereas the slight spacing between the outer periphery wall of the bushing and core and body.

Actually, therefore, the threaded engagement between the metal portion 3| of the spark plug core and the body I provides a better heat conducting path than between the bushing and the spark plug body, and the cooler the core tip the less will be the tendency for preignition to occur. On the contrary, the inner peripheral wall of the spark plug cavity encircling the spindle tip will be hotter than it would be otherwise, tending to deter deposits. At the same time, because of the long space between the spindle tip and bushing, the less chance is there for fouling and shorting out of the plug, despite accumulation of lead and carbon in this space. By keeping such space to a minimum volume by provision of the step in the bushing formed by the reduced bore 22 around the core tip, the less unburned fuel can penetrate into this space from which carbon and lead can be deposited. This construction, therefore, reduces fouling to a minimum without corresponding increase in the tendency for preignition to occur, which normally would result from the use of a hot type spark plug construction in such a situation.

The general results of a minimum accumulation of fouling deposits of carbon and lead comation at high speeds over extended periods, increased power, absence of preignition, reduced detonation, easier starting, smoother and longer idling, and more efiiciency fuel combustion than obtained with other types of spark plugs, have been ascertained by tests. Any deposit of carbon and lead compounds on the walls of the antechamber around or axially outwardly of the electrodes is very small, but after extended use of the spark plug some deposit occurs in the portion of the antechamber between the electrodes and the spark plugs inner end. Such deposit is found to be graduated axially, being heavier at the inner end of the spark plug and progressively lighter toward the electrodes.

I claim as my invention:

1. A spark plug comprising a body having an internal chamber converging toward the inner end of said body and opening through the inner end of said body by way of a restricted opening therein, a bushing received in said chamber and devoid of threaded interengagement with said body, the end of said bushing closer to the inner end of said body forming an inwardly projecting shoulder in said chamber facing toward the inner end of said body, an insulator received with in said bushing, spaced inwardly from said bushing substantially throughout within said body and having its inner end disposed adjacent to said inwardly projecting shoulder, a grounded electrode cooperating with said first electrode, and an an engine.

2. A spark plug comprising a body having an ceived within said bushing, spaced inwardly from 1 said bushing substantially throughout the entire length of said bushing and carrying a first electrode within said body and having its in ner end disposed adjacent to said inwardly projecting shoulder, a second electrode carried by the shoulder forming end of said bushing and cooperating with said first electrode, and an external shoulder on said body facing the inner end of said body and spaced therefrom at least substantially as far as said shoulder-forming end of said bushing is spaced from the inner end of said body, and said body being externally threaded substantially from said external shoulder toward the inner end of said body for reception in the spark plug port of an engine.

'3. In a spark plug, a body having an internal chamber opening through the inner end of said body by way of a restricted opening therein, a metal bushing reecived in said chamber and devoid of threaded interengagement with said body, the end of said bushing closer to the in-- her end of said body forming an inwardly projecting shoulder in said chamber facing toward the inner end of said body, an insulator received within and extending most of the way through the bushing bore spaced from the wall thereof to form a narrow annular portion of the internal chamber between said insulator and said bushing bore, means independent of said bushing securing said insulator in said body, a first electrode carried by said insulator adjacent to the shoulder-forming end of said bushing, and a grounded electrode carried by the shoulderforming end of said bushing and cooperating with said first electrode.

4. The spark plug defined in claim 3, in which the insulator is of decreasing size toward the inner end of the body, and the portion of the bushing bore adjacent to the insulator is of decreasing size toward the inner end of the body.

5. The spark plug defined in claim '3, in which the insulator is of stepped formation and the bushing bore is stepped generally correspondingly to the insulator.

6. A spark plug comprising a hollow metal body defining an antecharnber in the inner end thereof having a restricted aperature opening through the inner end of said body, an internal shoulder in the spark plug hollow facing away from the inner end of said body, a bushing having its exterior wall fitting loosely in the hollow of said spark plug and a ledge abutting said shoulder, an insulator received within and spaced from the inner periphery of said bushing and carrying a first electrode, means interengaged between said insulator and said body and effecting a good heat-conducting path therebetween, and a grounded electrode mounted on said bushing and disposed adjacent to said first electrode for forming a spark gap therebetween in said antechamber.

7. A spark plug comprising a hollow metal body defining an antechamber in the inner end thereof opening through the inner end of said body, a bushing having its exterior wall fitting loosely in the hollow of said spark plug, having its inner end spaced a substantial distance from the inner end of said body and having an opening in its inner end at least substantially as large as the opening in the inner end of said body, an insulator received within and extending most of the way through the bushing bore spaced from the wall thereof and carrying a first electrode, means interengaged between said insulator and said body and effecting a good heat-conducting path therebetween, and a grounded electrode supported from said body and disposed adjacent to said first electrode for forming a spark gap therebetween in said antechamber.

8. A spark plug comprising a hollow metal body defining an antechamber in the inner end thereof having a restricted aperture opening through the inner end of said body, an internal shoulder in the spark plug hollow facing away from the inner end of said body, a bushing, having its exterior wall fitting loosely in the hollow of said spark plug and a ledge abutting said shoulder, an insulator received within and extending most of the way through the bushing bore spaced from the wall thereof carrying an elongated first electrode within antechaznber spaced a substantial distance lengthwise of the electrode from such restricted antechamber aperture, means interengaged between said insulator and said body and effecting a good heat-conducting path therebetween, and a grounded electrode supported from body and disposed adjacent to said first electrode for forming a spark gap therebetween in said antechamber.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 981,752 Falwell Jan. 17, 1911 1,206,788 Colin Nov. 28, 1916 1,359,591 Grimes Nov. 23, 1920 1,390,014 Brewster Sept. 6, 1921 1,552,352 Shepherd Sept. 1, 1925 2,178,348 Ruthardt Oct. 31, 1939 

